Pulse tube refrigerator

ABSTRACT

A pulse tube refrigerator, includes a pulse tube; and a regenerator having a low temperature end, the low temperature end being in communication with a low temperature end of the pulse tube via a communicating path, wherein a heat exchanger is provided at the low temperature end side of the pulse tube in the communicating path; the heat exchanger includes a laminated body, the laminated body including at least first and second metal gauzes; the first and second metal gauzes include copper or a copper alloy; interfaces of the metal gauzes are diffusion-bonded to each other; and a side surface of the laminated body is diffusion-bonded to an internal wall forming the communicating path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based upon and claims the benefit of priorityof Japanese Patent Application No. 2010-010447 filed on Jan. 20, 2010,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to pulse tube refrigerators.

2. Description of the Related Art

Conventionally, a pulse tube refrigerator has been used for cooling anapparatus requiring a cryogenic temperature environment, such as a MRI(magnetic resonance imaging) apparatus.

In the pulse tube refrigerator, a cryogenic state is formed at lowtemperature ends of a regenerator and a pulse tube by repeatingoperations where coolant gas (for example, helium gas) as operatingfluid compressed by a compressor flows into the regenerator and into thepulse tube and operations where the operating fluid flows out from theregenerator and into the pulse tube and is received by the compressor.

A regenerator of the pulse tube refrigerator includes acylindrical-shaped member (cylinder) in which a regenerator material isprovided. A pulse tube includes a hollow cylindrical-shaped member(cylinder). Low temperature ends of the cylinder of the regenerator andthe cylinder of the pulse tube are in fluid communication with eachother via a communicating path. A cooling stage where a cooled body isconnected is provided in this position.

It is a normal practice that a heat exchanger is provided at a lowtemperature end side of the pulse tube. The heat exchanger includes alaminated body formed of metal gauzes or the like made of copper.

the pulse tube refrigerator may be degraded.

SUMMARY OF THE INVENTION

Accordingly, embodiments of the present invention may be to provide apulse tube refrigerator, including a pulse tube; and a regeneratorhaving a low temperature end, the low temperature end being incommunication with a low temperature end of the pulse tube via acommunicating path, wherein a heat exchanger is provided at the lowtemperature end side of the pulse tube in the communicating path; theheat exchanger includes a laminated body, the laminated body includingat least first and second metal gauzes; the first and second metalgauzes include copper or a copper alloy; interfaces of the metal gauzesare diffusion-bonded to each other; and a side surface of the laminatedbody is diffusion-bonded to an internal wall forming the communicatingpath.

Another aspect of the embodiments of the present invention may be toprovide a pulse tube refrigerator, including a pulse tube; and aregenerator having a low temperature end, the low temperature end beingin communication with a low temperature end of the pulse tube via acommunicating path, wherein a heat exchanger is provided at the lowtemperature end side of the pulse tube in the communicating path; theheat exchanger includes a laminated body and a housing, the laminatedbody including at least first and second metal gauzes; the first andsecond metal gauzes and the housing include copper or a copper alloy;interfaces of the metal gauzes are diffusion-bonded to each other; thelaminated body is received in the housing; and a side surface of thelaminated body is diffusion-bonded to an internal wall of the housing.

According to the embodiments of the present invention, it is possible toprovide a pulse tube refrigerator including a heat exchanger having heatexchangeability better than that of the conventional art.

Additional objects and advantages of the embodiments are set forth inpart in the description which follows, and in part will become obviousfrom the description, or may be learned by practice of the invention.The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe appended claims. It is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a pulse tube refrigerator of an embodimentof the present invention;

FIG. 2 is a cross-sectional view of an example of a heat exchanger;

FIG. 3 is an exploded schematic structural view of a laminated bodyincluded in the heat exchanger;

FIG. 4 is a cross-sectional view of another example of a heat exchanger;

FIG. 5 is an exploded schematic structural view of another laminatedbody included in the heat exchanger; and

FIG. 6 is an exploded schematic structural view of yet another laminatedbody included in the heat exchanger.

DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS

In a related art pulse tube refrigerator, the laminated body formed ofthe metal gauzes or the like made of copper, as the heat exchanger, issupplied at the low temperature end side of the pulse tube. The reasonwhy the metal gauzes are used is for preventing a big difference ofspeeds of the coolant gas when the coolant gas flows from theregenerator to the pulse tube. In other words, a flow smoothening effectof the coolant gas is improved by using the metal gauzes.

However, in a case where such a laminated body is supplied at the lowtemperature end side of the pulse tube so that the heat exchanger isformed, it may be difficult to make efficient thermal contact between aside surface of the laminated body and an internal wall of a groovewhere the laminated body is received. Because of this, depending on acontact state of the side surface of the laminated body and the internalwall of the groove, thermal resistance of an interface may bedrastically changed. As a result of this, an unstable state of the heatexchangeability may be generated so that the heat exchangeability of

Embodiments of the present invention may provide a novel and usefulpulse tube refrigerator solving one or more of the problems discussedabove.

More specifically, the embodiments of the present invention may providea pulse tube refrigerator including a heat exchanger having heatexchangeability better than that of the conventional art.

A description is given below, with reference to the FIG. 1 through FIG.6 of embodiments of the present invention.

FIG. 1 is a schematic view of a pulse tube refrigerator of an embodimentof the present invention.

As shown in FIG. 1, a pulse tube refrigerator 100 of an embodiment ofthe present invention includes a compressor 110, a regenerator 120, apulse tube 140, a cooling stage 180, and a buffer tank 190. Theregenerator 120 has a high temperature end 125 a and a low temperatureend 125 b. The pulse tube 140 has a high temperature end 145 a and a lowtemperature end 145 b.

An exhaust valve 110 a and an intake valve 110 b are connected to thecompressor 110. In addition, the compressor 110 is connected to the hightemperature end 125 a of the regenerator 120 via a gas flow path 112.

The regenerator 120 is formed of, for example, a hollow cylinder 121. Aregenerator material 122 is supplied inside the cylinder 121. Thecylinder 121 is made of, for example, stainless steel.

The pulse tube 140 is formed of, for example, a hollow cylinder 141 madeof stainless steel. A heat exchanger 149 a is provided at the hightemperature end 145 a side of the pulse tube 140. A heat exchanger 149 bis provided at the low temperature end 145 b side of the pulse tube 140.

The low temperature end 125 b of the regenerator 120 and the lowtemperature end 145 b of the pulse tube 140 come in contact with and arefixed to the cooling stage 180 made of, for example, copper. Inaddition, the low temperature end 125 b of the regenerator 120 and thelow temperature end 145 b of the pulse tube 140 are in communicationwith each other by a communicating path 182 provided in the coolingstage 180. The cooling stage 180 is thermally connected to a cooledsubject (not shown in FIG. 1) so that the cooled subject is cooled.

The buffer tank 190 is connected to the high temperature end 145 a ofthe pulse tube 140 via a gas flow path 192 and an orifice 194.

The high temperature end 125 a of the regenerator 120 and the hightemperature end 145 a of the pulse tube 140 are connected to a flange115 so that the regenerator 120 and the pulse tube 140 are fixed.

Next, operations of the pulse tube refrigerator having theabove-discussed structure are discussed.

First, in a state where the exhaust valve 110 a is opened and the intakevalve 110 b is closed, coolant gas having a high pressure is suppliedfrom the gas compressor 110 to the regenerator 120 via the exhaust valve110 a and the gas flow path 112. While the coolant gas flowing into theregenerator 120 is cooled by the regenerator material 122 so that atemperature of the coolant gas is decreased, the coolant gas passesthrough the communicating path 182 from the low temperature end 125 b ofthe regenerator 120. The coolant gas is further cooled by the heatexchanger 149 b provided at the low temperature end 145 b side of thepulse tube 140 so as to flow into the pulse tube 140.

At this time, coolant gas having a low pressure which exists in thepulse tube 140 in advance is compressed by the flowing cooling gas withthe high pressure. As a result of this, the pressure of the coolant gassituated in the pulse tube 140 becomes higher than a pressure of aninside of the buffer tank 190. The coolant gas passes through theorifice 194 and the gas flow path 192 so as to flow into the buffer 190.

Next, when the exhaust valve 110 a is closed and the intake valve 110 bis opened, the coolant gas in the pulse tube 140 passes through the lowtemperature end 145 b so as to flow into the low temperature end 125 bof the regenerator 120. Further, while the coolant gas cools theregenerator material 122, the coolant gas passes through the regenerator120. The coolant gas passes from the high temperature end 125 a throughthe gas flow path 112 and the intake valve 110 b so as to be received bythe compressor 110.

Here, the pulse tube 140 is connected to the buffer tank 190 via theorifice 194. Because of this, a phase of pressure change of the coolantgas and a phase of volume change of the coolant gas are changed with aconstant phase difference. Due to this phase difference, a cryogenicstate based on expansion of the coolant gas is formed at the lowtemperature end 145 b of the pulse tube 140. By repeating theabove-discussed operations, the pulse tube refrigerator 100 can cool thecooled subject connected to the cooling stage 180.

In the meantime, in the related art pulse tube refrigerator, a laminatedbody formed by metal gauzes made of copper is used as a heat exchangerprovided at the low temperature end side of the pulse tube. The reasonwhy such metal gauzes are used is to prevent generating big differencesin the speed of the coolant gas when the coolant gas flows from theregenerator to the pulse tube. In other words, a flow smoothening effectof the coolant gas is improved by using the metal gauzes. This laminatedbody is supplied to the low temperature end side of the pulse tube,after members forming the laminated body are fixed in order to preventshift of the members.

However, in the case where the heat exchanger has the above-mentionedstructure, even if the laminated body is formed with high precision, acertain gap may be formed between a side surface of the laminated bodyand an internal wall of the groove receiving the laminated body (thecommunicating path 182 in an example shown in FIG. 1). Therefore, it maybe difficult to always have precise thermal contact between the sidesurface of the laminated body and the internal wall of the groovereceiving the laminated body. In addition, because of this, depending onthe contact state of the side surface of the laminated body and theinternal wall of the groove receiving the laminated body, the thermalresistance at an interface may be drastically changed. Hence, anunstable state of the heat exchangeability may be generated so that theheat exchangeability of the pulse tube refrigerator may be degraded.

In order to solve the above-mentioned problem, after the laminated bodyis supplied in the groove, a side part of the laminated body may bebrazed at the internal wall of the groove.

However, in this way, even if the laminated body and the internal wallof the groove can be made to be in contact with each other at plural“points”, it may be difficult for the side part of the laminated body toentirely come in contact with the internal wall of the groove.Accordingly, this way cannot sufficiently achieve an inhibition effectof the thermal resistance and cannot solve the above-discussed problem.

On the other hand, according to the pulse tube refrigerator of theembodiment of the present invention, the heat exchanger 149 b providedat the low temperature end side 145 b of the pulse tube 140 isdiffusion-bonded to the internal wall of the groove receiving the heatexchanger 149 b.

With the above-mentioned structure of the heat exchanger 149 b, the sidepart of the heat exchanger 149 b always comes in contact with theinternal wall of the groove. Therefore, a problem of the related artwhere the thermal resistance is drastically changed and the heatexchangeability of the pulse tube refrigerator is degraded can bereduced or solved.

Details of the embodiment of the present invention are further discussedwith reference to FIG. 2 and FIG. 3.

FIG. 2 is a schematic cross-sectional view of the vicinity of a groove189 of the cooling stage 180 where the low temperature end 145 b of thepulse tube 140 is connected. In FIG. 2, a schematic cross section of anexample of the heat exchanger 149 b used for the embodiment of thepresent invention is used. FIG. 3 is an exploded schematic structuralview of a laminated body 150 included in the heat exchanger 149 b asearlier shown in FIG. 1.

As shown in FIG. 2, the heat exchanger 149 b is formed in the groove 189of the cooling stage 180. The heat exchanger 149 b includes thelaminated body 150. The side surface of the laminated body 150 isdiffusion-bonded to an internal wall 184 of the groove 189.

As shown in FIG. 3, in a normal case, the laminated body 150 is made bylaminating plural metal gauzes made of copper or a copper alloy(hereinafter “made of copper” in a lump). In the example shown in FIG.3, the laminated body 150 is formed by laminating a first metal gauze152A, a second metal gauze 152B, a third metal gauze 152C, . . . and annth metal gauze 152N. Here, the laminated body 150 may be made of asingle metal gauze 152A made of copper. Contact interfaces of the firstmetal gauze 152A, the second metal gauze 152B, the third metal gauze152C, . . . , and the nth metal gauze 152N are diffusion-bonded.Therefore, thermal contact of the interfaces is improved so that thethermal resistance of the interfaces is made small.

The heat exchanger 149 b is formed in the groove 189 of the coolingstage 180 in, for example, the following way.

First, the metal gauzes 152A, 152B, 152C, . . . , and 152N made ofcopper are laminated. Next, the formed laminated body 150 is provided inthe groove 189 of the cooling stage 180. After that, a “diffusionbonding process” is applied for the cooling stage 180 so that the heatexchanger 149 b is formed.

Here, the “diffusion bonding process” is a method where atomicinterdiffusion is generated at the interfaces between the gauzes152A-152N by heating so that the interface bonding is made. Normally,the diffusion bonding process of this embodiment is performed at atemperature in a range of between approximately 800° C. andapproximately 1080° C. (for example, approximately 1000° C.).

By such a diffusion bonding process, at the same time when theinterfaces of the metal gauzes 152A-152N are adhered and bonded, theside surface of the laminated body 150 is diffusion-bonded to theinternal wall 184 of the groove 189.

The diffusion bonding process between the metal gauzes 152A-152N may beperformed before the diffusion bonding process of the laminated body 150and the internal wall 184 of the groove 189 (namely “two stages” of thediffusion bonding process).

With the structure of the heat exchanger 149 b compared to a case wherethe laminated body 150 is supplied to the groove 189 later, contactbetween the heat exchanger 149 b and the cooling stage 180 can beimproved so that the thermal resistance between the heat exchanger 149 band the cooling stage 180 can be inhibited.

Here, in an example shown in FIG. 3, a mesh or an opening length of eachof the metal gauzes 152A, 152B, 152C, . . . , and 152N made of coppermay be substantially equal to the others or different from the others.

In this specification, the “mesh” means the number of stitches situatedin a length of approximately 1 inch (approximately 25.4 mm.) The“opening length” means a length between neighboring wires of the metalgauze (the length of a gap).

In a case where the opening lengths of the metal gauzes 152A, 152B,152C, . . . , and 152N are different, the opening lengths may be greatercontinuously or gradually (for example, in a step manner) in the orderfrom the first metal gauze 152A to the Nth metal gauze 152N. In thiscase, the first metal gauze 152A having short opening lengths, comparedto the Nth metal gauze 152A having long opening lengths, is provided ata side far from the low temperature end 125 b of the regenerator 120 (aside near the pulse tube 140). As a result of this, when the coolant gasflows from the regenerator 120 to the pulse tube 140, a big change ofthe flow speed of the coolant gas may not be generated so that a moreeffective flow smoothening effect can be achieved.

A total number of the metal gauzes 152A-152N may differ depending on thethickness of each of the metal gauzes. The total number of the metalgauzes 152A-152N may be in a range between 2 and 200 (for example, 100).

The mesh of each of the metal gauzes made of copper is normally in arange between #16 and #300, By converting the opening length of themetal gauzes 152A-152N, this is in a range between approximately 1.14 mmand approximately 0.05 mm. It may be preferable that the meshes of themetal gauzes made of copper be in a range between #60 and #150 (which isthe opening length in a range between approximately 0.303 mm andapproximately 0.104 mm).

A rolling process may be applied to the metal gauzes 152A-152N. A casewhere the rolling process is applied to the metal gauzes is discussedat, for example, Japanese Patent Application Laid-Open Publication No.2003-28526. As shown in FIG. 2(A) of Japanese Patent ApplicationLaid-Open Publication No. 2003-28526, by applying the rolling process tothe metal gauzes, a contact area of the metal gauzes is increased. As aresult of this, thermal contact resistance of the metal gauzes becomessmall so that the heat exchange efficiency rate is improved. Thethickness of the metal gauzes after the rolling process is applied is ina range between approximately 0.4 mm through approximately 0.99 mm whenthe thickness of the metal gauze before the rolling process is appliedis 1 mm. It is preferable that the thickness be in a range betweenapproximately 0.6 mm through approximately 0.8 mm.

In the example shown in FIG. 2, the side surface of the heat exchanger149 b is diffusion-bonded to the internal wall 184 of the groove 189 ofthe cooling stage 180. However, the present invention is not limited tothis structure. For example, the side surface of the heat exchanger 149b may be diffusion-bonded to the internal wall 184 at the lowtemperature end 145 b of the cylinder 141 forming the pulse tube 140.

Next, a structure of another heat exchanger 149 b-2 is discussed withreference to FIG. 4. FIG. 4 schematically shows a cross section of thevicinity of the groove 189 of the cooling stage 180 where the lowtemperature end 145 b of the pulse tube 140 is connected. A schematiccross-section of an example of the heat exchanger 149 b-2 used for theembodiment of the present invention is shown in FIG. 4.

As shown in FIG. 4, the heat exchanger 149 b-2 is formed in the groove189 of the cooling stage 180. The heat exchanger 149 b-2 includes alaminated body substantially the same as that of the heat exchanger 149b. However, the heat exchanger 149 b-2 further includes a housing 159receiving the laminated body 150 formed of metal gauzes. The housing 159is made of copper or a copper alloy. In addition, openings are formed inan upper surface and a lower surface of the housing 159. A size of aside surface of the housing 159 substantially corresponds to an internaldiameter of the groove 189. A side surface of the laminated body 150formed of the metal gauzes is diffusion-bonded to the internal wall 184of the side surface of the housing 159.

The heat exchanger 149 b-2 can be formed by laminating the metal gauzes152A, 152B, 152C, . . . , and 152N and supplying the metal gauzes 152A,152B, 152C, . . . , and 152N into the housing 159, and then by applyingthe diffusion bonding process to the metal gauzes 152A, 152B, 152C, and152N together with the housing 159. After that, the housing 159 isprovided in the groove 189 of the cooling stage 180 and the housing 159is brazed to the internal wall 184 of the groove 189 of the coolingstage 180.

In a case where the housing 159 and the internal wall 184 are brazed toeach other, compared to a case where the laminated body and the internalwall are directly brazed to each other, degrees of adhesion and contactof the housing 159 and the internal wall 184 at the contact interfaceare better. Since end parts of plural members exist at the side surfaceof the laminated body, it may be difficult to sufficiently smooth theside surface of the laminated body with high precision. On the otherhand, since the housing 159 is formed of a single member, it isrelatively easy to smooth the side surface of the housing with highprecision.

Accordingly, with the structure shown in FIG. 4, compared to the relatedart heat exchanger, it is possible to improve the thermalcontact-ability between the heat exchanger 149 b-2 and the cooling stage180 so that the thermal resistance between the heat exchanger 149 b-2and the cooling stage 180 can be effectively inhibited.

In the example shown in FIG. 4, the heat exchanger 149 b-2 is directlyprovided in the groove 189 of the cooling stage 180. However, thepresent invention is not limited to this structure. For example, theoutside of the heat exchanger 149 b-2 may come in contact with the lowtemperature end 145 b side of the cylinder 141 forming the pulse tube140. In this case, the housing 159 of the heat exchanger 149 b-2 isbrazed to the internal wall of the cylinder 141.

In the above-discussed example, the cases where the heat exchanger 149 band the heat exchanger 149 b-2 includes the laminated body 150 formed ofthe metal gauzes made of copper is explained. However, the presentinvention is not limited to this structure.

FIG. 5 shows a structure of another laminated body used for the heatexchanger 149 b and the heat exchanger 149 b-2.

In the example shown in FIG. 5, the laminated body 150A is formed bylaminating a first metal gauze 153A, a second metal gauze 153B, a thirdmetal gauze 153C, a fourth metal gauze 153D, . . . and an nth metalgauze 153N in this order. In the laminated body 150A, as well as thelaminated body 150 discussed above, contact interfaces of the firstmetal gauze 153A, the second metal gauze 1538, the third metal gauze153C, the fourth metal gauze 153D, . . . and the nth metal gauze 153Nare diffusion-bonded.

While the second metal gauze 153B, the third metal gauze 153C, thefourth metal gauze 153D, . . . and the nth metal gauze 153N are made ofcopper, the first metal gauze 153A is made of metal or an alloyexcluding copper. For example, the first metal gauze 153A may be made ofstainless steel (SUS 304, 316, or the like), nickel, or the like.Stainless steel or nickel has rigidity higher than that of copper.Therefore, in a case where the first metal gauze 153A is made ofstainless steel or nickel, it is possible to improve rigidity of thelaminated body 150A being finally formed. Hence, the likelihood is smallof the laminated body 150A being deformed due to a pressure of thecoolant gas when the pulse tube refrigerator 100 is formed.

In addition, the first metal gauze 153A may have meshes relativelylarger than those of other metal gauzes (opening lengths relativelyshorter than those of other metal gauzes). In this case, the laminatedbody 150A is provided in the groove 189 so that the first metal gauze153A is provided at a far side from the low temperature end 125 b of theregenerator 120 (an upper side in the examples shown in FIG. 2 and FIG.4). As a result of this, a more effective flow smoothening effectrelative to the coolant gas reciprocating between the regenerator 120and the pulse tube 140 can be achieved.

Normally, it is difficult to manufacture the metal gauze made of copperand having large meshes and short opening lengths due to limitations ofmanufacturing techniques and costs. For example, in the case of themetal gauze made of copper, a maximum value of the mesh is approximately#100 and a minimum value of the opening length is approximately 0.134 mmthrough approximately 0.154 mm. However, it is relatively easy tomanufacture the metal gauze made of non-copper metal such as stainlesssteel and having large meshes and short opening lengths. Therefore, bycombining two kinds of materials, it is possible to perform a wide rangeof design relative to flow smoothening of the heat exchangers 149 b and149 b-2.

The mesh of the first metal gauze 153A is in a range between #30 and#500. By converting the opening length of the metal gauze, this is in arange between approximately 0.577 mm and approximately 0.026 mm. It maybe preferable that the mesh of the first metal gauzes 153A be in a rangebetween #60 and #400 (which is the opening length in a range betweenapproximately 0.253 mm and approximately 0.034 mm). The mesh of thesecond metal gauzes 153B through the nth metal mesh 153N may be in arange between #16 and #300. By converting the opening length of themetal gauze, this is in a range between approximately 1.14 mm andapproximately 0.05 mm. It may be preferable that the mesh of the secondmetal gauze 153B through the nth metal mesh 153N is in a range between#60 and #150 (which is the opening length in a range betweenapproximately 0.303 mm and approximately 0.104 mm). As discussed above,the meshes or the opening lengths of the second metal gauzes 153Ethrough the nth metal mesh 153N may be equal to or different from eachother.

A total number of the metal gauzes may differ depending on thethicknesses of the metal gauzes. The total number of the metal gauzesmay be in a range between 2 and 200 (for example, 100).

As discussed above, the laminated body 150A is provided in the groove189 of the cooling stage 180 and then the diffusion bonding process isapplied, so that the heat exchanger 149 b is formed. Alternatively, thelaminated body 150A is provided in the housing 159 and then thediffusion bonding process is applied. After that, the housing 159 isprovided in the groove 189 of the cooling stage 180 and the housing 159and the internal wall 184 are brazed to each other, so that the heatexchanger 149 b-2 is formed. The diffusion bonding process is performedat a temperature in a range between approximately 800° C. andapproximately 1080° C. (for example, approximately 1000° C.).

FIG. 6 shows a structure of another laminated body used for the heatexchanger 149 b and the heat exchanger 149 b-2.

In the example shown in FIG. 6, a laminated body 150B is formed bylaminating a first metal gauze 154A, a second metal gauze 154B, a thirdmetal gauze 154C, a fourth metal gauze 154D, . . . and an nth metalgauze 154N in this order. In the laminated body 150B, as well as thelaminated body 150 and the laminated body 150A discussed above, contactinterfaces of the first metal gauze 154A, the second metal gauze 154B,the third metal gauze 154C, the fourth metal gauze 154D, . . . and thenth metal gauze 153N are diffusion-bonded.

The second metal gauze 154B, the fourth metal gauze 154D, and a sixthmetal gauze 154F through the nth metal gauze 154N are made of copper. Onthe other hand, three metal gauzes, namely, the first metal gauze 154A,the third metal gauze 154C, and a fifth metal gauze 154E are made ofmetal or an alloy excluding copper. For example, the first metal gauze153A, the third metal gauze 154C, and the fifth metal gauze 154E aremade of stainless steel (SUS 304, 316, or the like), nickel, or thelike. The first metal gauze 154A, the third metal gauze 154C, and thefifth metal gauze 154E may be made of the same material or differentmaterials.

In a structure shown in FIG. 6, a cycle where a metal gauze made ofnon-copper and a metal gauze made of copper are mutually laminated isrepeated three times.

Three metal gauzes, namely, the first metal gauze 154A, the third metalgauze 154C, and the fifth metal gauze 154E have meshes relatively largerthan those of other metal gauzes (opening lengths relatively shorterthan those of other metal gauzes).

For example, the meshes of the first metal gauze 154A, the third metalgauze 154C, and the fifth metal gauze 154E are in a range between #30and #500. By converting the opening length of the metal gauze, this isin a range between approximately 0.577 mm and approximately 0.026 mm. Itmay be preferable that the meshes of the first metal gauzes 154A, thethird metal gauzes 154C, and the fifth metal gauzes 154E be in a rangebetween #60 and #400 (which is the opening length in a range betweenapproximately 0.253 mm and approximately 0.034 mm). On the other hand,the meshes of the metal gauzes 154B, 154D, and 154F through 154N are ina range between #16 and #300. By converting the opening length of themetal gauze, this is in a range between approximately 1.14 mm andapproximately 0.05 mm. It may be preferable that the meshes of the metalgauzes 154B, 154D, and 154F through 154N are in a range between #60 and#150 (which is the opening length in a range between approximately 0.303mm and approximately 0.104 mm). The meshes or the opening lengths of themetal gauzes made of copper may be equal to or different from eachother. In a case where the opening lengths of the metal gauzes 154Bthrough 154N are different, the opening lengths may be greatercontinuously or gradually (for example, in a step manner) in the orderfrom the second metal gauze 154B to the Nth metal gauze 154N.

A total number of the metal gauzes may differ depending on the thicknessof each of the metal gauzes. The total number of the metal gauzes may bein a range between 2 and 200 (for example, 100).

The laminated body 150B shown in FIG. 6 is provided in the cooling stagegroove 189 so that the first metal gauze 154A is provided at a side farfrom the communicating path 182 of the cooling stage 180 (an upper sidein the examples shown in FIG. 2 and FIG. 4).

The laminated body 150B, where there are three metal gauzes made ofnon-copper and the cycle number C is three, is discussed in the exampleshown in FIG. 6. However, in the laminated body 150B, there is nolimitation of the number of the metal gauzes made of non-copper and thecycle number C. The number of the metal gauzes may be, for example, two,four or equal to or greater than six. In addition, the cycle number Cmay be, for example, two, four or equal to or greater than six. Forexample, mutual arrangement of the metal gauzes made of non-copper andthe metal gauzes made of copper may be repeated from the first metalgauze to the nth metal gauze (in the entirety of the laminated body150B).

Other objects, features, and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings. For example, in theabove-discussed example, the pulse tube refrigerator 100 is asingle-stage type pulse tube refrigerator. However, the presentinvention can be applied to a multi-stage type pulse tube refrigeratorsuch as two-stage type or three-stage type pulse tube refrigerator.

In the meantime, inventors of the present invention actually operatedthe pulse tube refrigerator, with normal conditions, where the heatexchanger 149 b shown in FIG. 2 is formed in the groove of the coolingstage 180, so as to measure the temperature of the cooling stage 180. Inaddition, the laminated body 150A shown in FIG. 5 was used as thelaminated body of the heat exchanger 149 b. A metal gauze, made of SUS304, whose mesh is #250 was used as the metal gauze 153A situated at thetop. In addition, metal gauzes, made of copper, whose meshes are #80were used as the metal gauzes situated at second and subsequent stages.

As a result of the measurement, it was found that the temperature of thecooling stage 180 was approximately 36.4 K. On the other hand, the samemeasurement was made of a pulse tube refrigerator where a conventionalheat exchanger (the laminated body made of copper and having meshes of#80 provided, where the side part of the laminated body is notdiffusion-bonded to the internal wall of the groove) was provided in thegroove of the cooling stage. It was found that the temperature of thecooling stage was approximately 40.2 K in this case.

As a result of the measurements, it was confirmed that cooling abilitiesare improved in the pulse tube refrigerator 100 of the embodiment of thepresent invention compared to the conventional pulse tube refrigerator.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority orinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

The present invention can be applied to a single-stage type or amulti-stage type pulse tube refrigerator which is applied to a lowtemperature system such as a nuclear magnetic resonance diagnosticapparatus, a superconducting magnet apparatus, or a cryopump.

1. A pulse tube refrigerator, comprising: a pulse tube; and aregenerator having a low temperature end, the low temperature end beingin communication with a low temperature end of the pulse tube via acommunicating path, wherein a heat exchanger is provided at the lowtemperature end side of the pulse tube in the communicating path; theheat exchanger includes a laminated body, the laminated body includingat least first and second metal gauzes; the first and second metalgauzes include copper or a copper alloy; interfaces of the metal gauzesare diffusion-bonded to each other; and a side surface of the laminatedbody is diffusion-bonded to an internal wall forming the communicatingpath.
 2. The pulse tube refrigerator as claimed in claim 1, wherein thelaminated body includes a third metal gauze, the third metal gauze beingsituated at a top of the laminated body, the third metal gauze includingmetal other than the copper or the copper alloy; the interfaces of themetal gauzes are diffusion-bonded to each other; and the laminated bodyis provided in the communicating path so that a side of the third metalgauze is situated furthest from the low temperature end of theregenerator.
 3. The pulse tube refrigerator as claimed in claim 2,wherein the laminated body includes a fourth metal gauze, the fourthmetal gauze being situated at a top of the laminated body, the fourthmetal gauze including metal other than the copper or the copper alloy;the interfaces of the metal gauzes are diffusion-bonded to each other;and the laminated body is formed by laminating the third metal gauze,the first metal gauze, the fourth metal gauze, and the second metalgauze.
 4. The pulse tube refrigerator as claimed in claim 3, wherein thelaminated body is formed by laminating six or more of the metal gauzes;the laminated body has a structure where the metal gauzes made of metalother than the copper or the copper alloy and the metal gauzes made ofthe copper or the copper alloy are mutually and repeatedly provided; andthe interfaces of the metal gauzes are diffusion-bonded to each other.5. The pulse tube refrigerator as claimed in claim 3, wherein openingareas of the metal gauzes made of the metal other than the copper or thecopper alloy are substantially equal to each other.
 6. The pulse tuberefrigerator as claimed in claim 3, wherein an opening area of the metalgauzes made of the metal other than the copper or the copper alloy issmaller than an opening area of the metal gauzes made of the copper orthe copper alloy.
 7. The pulse tube refrigerator as claimed in claim 3,wherein an opening area of the metal gauzes made of the metal other thanthe copper or the copper alloy is in a range between approximately 0.02mm and approximately 0.58 mm.
 8. The pulse tube refrigerator as claimedin claim 2, wherein the metal other than the copper or the copper alloyis stainless steel or nickel.
 9. The pulse tube refrigerator as claimedin claim 1, wherein a rolling process is applied to the metal gauzes.10. The pulse tube refrigerator as claimed in claim 1, wherein athickness of the metal gauzes after a rolling process is applied is in arange between approximately 0.4 mm through approximately 0.99 mm whenthe thickness of the metal gauzes before the rolling process is appliedis 1 mm.
 11. The pulse tube refrigerator as claimed in claim 1, whereinan opening area of the metal gauzes made of the copper or the copperalloy is in a range between approximately 0.05 mm and approximately 1.14mm.
 12. The pulse tube refrigerator as claimed in claim 1, whereinopening areas of the metal gauzes made of the copper or the copper alloyare substantially equal to each other.
 13. The pulse tube refrigeratoras claimed in claim 1, wherein opening areas of the metal gauzes made ofthe copper or the copper alloy are continuously or gradually decreasedfrom the metal gauze closest to the low temperature end of theregenerator toward a laminating direction of the laminated body.
 14. Apulse tube refrigerator, comprising: a pulse tube; and a regeneratorhaving a low temperature end, the low temperature end being incommunication with a low temperature end of the pulse tube via acommunicating path, wherein a heat exchanger is provided at the lowtemperature end side of the pulse tube in the communicating path; theheat exchanger includes a laminated body and a housing, the laminatedbody including at least first and second metal gauzes; the first andsecond metal gauzes and the housing include copper or a copper alloy;interfaces of the metal gauzes are diffusion-bonded to each other; thelaminated body is received in the housing; and a side surface of thelaminated body is diffusion-bonded to an internal wall of the housing.